Coated electrode for arc welding



Patented July- 6, 1937 UNITED STATES PATENT OFFICE signor to The LincolnElectric Company,

Cleveland, Ohio, a corporation of Ohio No Drawing. Application January30, 1932,

- Serial No. 589,983

2 Claims.

The present improvements, having to do with coated electrodes for arcwelding, have more particular regard to coatings suitable for metal andspeciflcallyjiron electrodes known commercially as weld-rod. For certainuses it is found satisfactory to provide such weld-rod. simply with awash coating, e. g., of a soap mixture, such coating making it easier tohold the arc. However, inother fields of use, it is essential and inpractically all cases desirable to provide a coating on the weld-rodthat will perform certain definite functions, .1. e., produce certain.desired effects in the welding operation. In particular it has beenfound desirable in many cases to sup;- ply an alloying ingredient to theweld metal as it is deposited in the seam or otherwise applied to thework, since it has been found that this will measurably increase thestrength of the welded joint. Such ingredient can be more convenientlysupplied in a coating on the rod than by including the alloyingingredient in the rod itself. It has alsobeen found important that aprotective slag covering be deposited over the molten weld metal notonly to prevent too rapid cooling of the latter, which may induceundesirable strains, but also to protect such metal before it sets fromexposure to the atmosphere with consequent harmful absorption of oxygenand nitrogen. Such slag forming material, as well as ingredients whichmay act directly as deoxldizers of the molten metal, are likewise mostconveniently included in the coating on the weldrod.

. Still other ingredients are desirably employed in such a coating inorder to retard the rate of fusion or combustion of the coating as wellas.

to mechanically bind the several ingredients into a hard durable coatingwhich will withstand the handling to which the coated weld-rod issubiected during manufacture and transportation and incidentally to use.Kaolin or clay is generally used as such combustion retardingingreclient and sodium silicate as such binder.

A certain minimum amount of each of the foregoing types of inorganicsubstances is necessary in the coating for best results. However, anyamount in addition to this is detrimental, tending to form too much slagduring thewelding operation, which results in slag inclusions in theweld, undercutting at the edge of the weld, depressions in the surfaceof the deposit and difficulty in cleaning off the resulting slag.

Finally, as-taught by Cravens (U. S. Patents Nos. 1,260,875 and1,260,989), it has been recognized as desirable to surround the are by anonoxidizing, insulating, gaseous vapor envelope, this not only toprevent lateral diffusion and dissipation ofheat but also to protect thehighly heated molten metal, as it is transferred from the end of the rodto the work, against contact with the atmosphere with consequentobjectionable absorption of gases. While the use of carbohydratematerial, specifically in the form of a cotton cord wound upon theweld-rod, is described in the aforesaid Cravens patents, and while otherequivalent organic materials such as paper pulp, wood pulp and woodflour, both in its natural state and chemically treated to remove thelignins, resins, etc., are described in various later patents, althoughnot always with a full appreciation of the function of these materialsin thus producing an insulating, non-oxidizing vapor in weldingproximity to the work, I have discovered that there are other importantconditions attending the use of such organic material, irrespective ofits particular source or character.

More especially I have found that the volume per unit weight of suchorganic constituents is an important factor in the securing ofsatisfactory results from a coating of the type described. In addition Ihave found that the proper proportioning of such organic constituents tothe several inorganic constituents employed, as well as theproportioning of the latter among themselves, is a factor of greatimportance in influencing the character of the slag deposited on theweld.

The object of the present invention, accord ingly, is to provide acoating composed of inorganic and organic materials of the typesindicated which will'both provide an effective shielding atmospherearound the arc and produce a fluffy slag that will afford a satisfactoryprotec tion for the weld and at the same time be readily removable aswell as eliminate slaginclusions, undercutting and other objectionableconditions. To the accomplishment of the foregoing and related ends, theinvention, then, consists of the means hereinafter fully described andparticularly pointed out in the claims, the following descriptionsetting forth in detail one approved combination of ingredientsembodying my invention, such disclosed means constituting, however, butone of various forms in which the principle of the invention may beused.

As examples of the alloying ingredients which may be desirably, althoughnot necessarily, in-

the latter purpose more specifically, titanium dioxide is desirablyemployed. In addition to the foregoing ingredients, a substantial amountof a compound such as kaolin, capable of forming a slag of highviscosity under the arc temperatures, is employed, together with asuitable refractory binder such as asbestos fiber and sodium silicate orwater-glass, the latter in the form of a solution in water.

For the organic constituent, as indicated above, a variety of materialsare available, these being preferably carbohydrates. Cotton of course issubstantially pure alpha-cellulose and is a most satisfactoryingredient, whether employed in the form of a cord wound around theelectrode or as cotton lint or chemically prepared alpha-cellulose. Thesame is true of paper pulp or wood pulp or flour where such wood pulp orflour has been chemically treated to eliminate the resins, etc.,although where the other conditions hereinafter set forth are observed,such elimination is not as important as has heretofore been assumed.

The amount of shielding atmosphere produced by the organic constituentsthus incorporated in the coating I have found depends upon the weight ofsuch constituents. A certain minimum amount of shielding atmosphere isof course essential in order to prevent oxidation of the weldmetal andto shield it from the nitrogen. of the air. However, an excess oforganic constituents is detrimental in that the latter do not burncompletely and tend to cause the formation of gas holes in the weld.

On the other hand, since-a definite thickness of coating on the weld-rodis necessary in order properly to confine and direct the arc, it isevident that the proportion of organic to inorganic constituents in thecoating depends not only upon their proportion by weight in the mixture,but" also to a great extent upon their respective volumes per unit ofweight. Accordingly, since the volume per unit weight of the inorganicconstituents is fairly constant, I have concluded that it is of theutmost importance in theproper design of a coating to pay particularattention to the volume per unit weight of the particular organicmaterial used. Now, the materials generally used for this purpose varyin volume per unit weight from about 1 cubic centimeter per gram toabout 3 cubic centimeters per gram' in their air-dried state. This maybe conveniently measured by weighing a given amount of the material intoa graduated cylinder and tapping the bottom of the latter on a block ofwood until the surface of the material settles down to its minimumheight. The volume may then be read directly in cubic centimeters.Organic materials which are suitable as fiux constituents can beproduced in a light fiuffy fibrous form which, when measured in themanner outlined above, will have volumes per gram weight as high as 20cubic centimeters. I have found, however, that best results are obtainedif the organic material used in the coating has a volume of 3.5 to 6cubic centimeters per gram weight, when such material containsapproximately 10% moisture. An organic material having this volume perunit weight prorluces a coating which enables the correct weight of suchmaterial to be employed without increasa lesser volume per gram thanthat indicated above as desirable.

If wood pulp is selected as the organic material for use in theforegoing mixture it should have a density corresponding with a volumeof from 3.5 to 6 cubic centimeters per gram weight determined in themanner set forth above. In place of such wood pulp, alpha-cellulose inits ordinary commercial form may be obtained having substantially thesame density, and this is als true of certain grades of cotton lint.

The foregoing organic and inorganic ingredients may be added to eachother in any desired order as most convenient and then thoroughlyintermixed. It should be stated that the-sodium silicate solution willcontain approximately 40% of such silicate but more or less water may beused in such solution, or, if necessary, additional water may be addedto the mixture in order to produce a paste of the proper consistency topermit its extrusion or application to the metal wire or rod. Thecoating after being dried. at ordinary or slightly elevated temperaturesin the air will firmly adhere to the metal without baking and besufficiently hard and resistant to withstand such handling as isordinarily encountered in the handling and use of these coatedelectrodes.

Other modes of applying the principle of'my invention may be employedinstead of the one explained, change being made as regards the materialsemployed, provided the ingredients stated by any of the following claimsor the equivalent of such stated ingredients be employed.

I therefore particularly point out and distinctly.

cellulosic material characterized by the fact that substantially all ofthe cellulosic material present in the covering before being combinedwith the remaining ingredients of the covering is in. such state thatwhen settled together in an air dried state and containing approximately10% moisture, one gram of the material will have a. volume ofapproximately 5 cubic centimeters.

THEOPHIL E. JERAB-EK.

